This invention relates to cores for housingless oil coolers for automobiles and the like and, more particularly, to cores for housingless oil coolers which are formed by stacking plate members.
Japanese Published Unexamined Utility Model Applications Nos. 125870/1987 and 74973/1988 disclose housingless oil coolers formed by stacking plate members of the type shown in FIGS. 1-3 of the drawings herein. As shown in FIG. 1, a housingless oil cooler has a core 11 which is formed by alternately stacking first and second plates 13 and 15 of stainless steel having different shapes so that cooling water passageways 17 and oil passageways 19 are formed alternately therebetween.
The core 11 of such conventional oil coolers is quite heavy because it contains a number of stainless steel plates 13 and 15 as described above. This interferes with the desired reduction of the total weight of an automobile. Therefore, there has been a strong demand for a light-weight core for a housingless oil cooler which is made of a coated aluminum material.
However, the manufacture of a core such as the core 11 of a conventional housingless oil cooler using a coated aluminum material gives rise to the following difficulties: The coated aluminum material, as shown in FIG. 2, comprises an aluminum base layer 21, a sacrificial corrosion layer 23 on one side of the base layer 21, and a brazing filler metal layer 25 on the other side of the base layer. Such coated aluminum material is pressed to form the first plates 13 and the second plates 15, which are then stacked to provide the core as shown in greater detail in FIG. 3. In that illustration, a space X is defined by the sacrificial corrosion layer 23 of the second plate 15 and the brazing filler metal layer 25 of the first plate 13 to provide a cooling water passageway. If highly corrosive cooling water is used in the cooling water passageway X, however, the brazing filler metal layer 25 of the first plate 13 suffers from pit corrosion, causing a number of pinholes to be formed in that plate
On the other hand, a space Y in FIG. 3 defined by the sacrificial corrosion layer 23 of the first plate 13 and the brazing filler metal layer 25 of the second plate 15 may be used as a cooling water passageway. In that case, if highly corrosive cooling water is used the brazing filler metal layer 25 of the second plate 15 suffers from pit corrosion, causing pinholes to be formed in that plate.
In the core of a conventional housingless oil cooler, the plates 13 and 15 are arranged in this way to make use of o the brazing of those plates, and therefore each cooling water passageway is bounded by the brazing filler metal layer 25 of one of the plates 13 and 15. This brazing filler metal layer 25 is subject to attack by corrosion, thus reducing the service life of the core.
FIGS. 4 and 5 show conventional core structures based on modifications of the first and second plates 13 and 15. These plates 13 and 15 are formed with the same configuration as those shown in FIG. 3, but they are coated differently so that, when they are stacked, the brazing filler metal layers 25 are in contact with each other, and accordingly the sacrificial corrosion layers 23 are in contact with each other. However, this arrangement has the disadvantage that, where only the sacrificial corrosion layers 23 are in contact with each other, the plates cannot be bonded together.